Arrangement provided with some combustion flash bulbs

ABSTRACT

The invention relates to an arrangement provided with some series-arranged combustion flash bulbs which can be ignited one after the other. According to the invention the succession of the flashes is obtained by choosing the resistive values of heating wires present in the flash bulbs to be unequal prior to flashing, and to have a low resistance of the flashed bulbs.

Unite States Bok et a1.

atent [191 1451 Nov. 11, 19 75 ARRANGEMENT PROVIDED WITH SOME COMBUSTION FLASH BULBS [75] Inventors: Johannes Gerardus Bok; Petrus Johannes Julius Witterick, both of Emmasingel, Eindhoven,

Netherlands [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: Apr. 24, 1974 [211 App]. No.: 463,730

[30] Foreign Application Priority Data May 1. 1973 Netherlands 7306019 [52] US. Cl. 431/95 A; 240/13 [51] Int. Cl.- F21K 5/02 [58] Field of Search 431/93-95.

[56] References Cited UNITED STATES PATENTS 3.443.875 5/1969 Herrmarm 431/95 A Primary E.\'anziner.lohn J. Camby Assistant Exanziner-Henry C. Yuen Attorney, Agent, or Firnt-Frank R. Trifari ABSTRACT The invention relates to an arrangement provided with some series-arranged combustion flash bulbs which can be ignited one after the other.

According to the invention the succession of the flashes is obtained by choosing the resistive values of heating wires present in the flash bulbs to be unequal prior to flashing, and to have a low resistance of the flashed bulbs.

10 Claims, 2 Drawing Figures 5 s 7 M m N v v v US. Patent Nov. 11, 1975 ARRANGEMENT PROVIDED WITH SOME COMBUSTION FLASH BULBS The invention relates to an arrangement provided with at least two series-arranged combustion flash bulbs which bulbs can be ignited one after the other and in which each of the bulbs includes a heating wire and an ignition paste, a means being provided in at least one bulb to render the internal resistance of said bulb one ohm at a maximum after flashing, the thermal capacities of the heating wires of the bulbs being substantially equal.

The thermal capacity of the heating wire is understood to mean the energy (for example, expressed in wattsecond or in joule) to be produced with an electrical current through this heating wire in order to raise the temperature of this wire by one degree Celcius.

In the said flash bulbs it is important how much energy must be produced to bring the heating wire from the ambient temperature to the ignition temperature of the ignition paste.

Since the time interval between the initiation of the current through the heating wire and the moment of reaching the ignition temperature of the ignition paste is very short, namely in the order of 0.5 millisecond, the heat conducted away from the thin heating wires commonly used for this purpose is negligibly small during this time interval. This means that the required energy for bringing the heating wire from the ambient temperature (room temperature) to the ignition temperature of the ignition paste is substantially equal to the product of the above-mentioned thermal capacity and the difference between the said ignition temperature and the ambient temperature.

A known arrangement of the kind mentioned above is described, for example, in Netherlands Patent Application No. 6915056.

A drawback of the said known arrangement is that prior to flashing the greater part of the heating wires of the bulbs is to be shunted by branches which have a relatively low resistive value. This is necessary to provide the next bulb to be flashed with current. This, however, makes the electrical circuit of the known arrangement complicated.

The invention has for its object to provide an arrangement of the kind described in the preamble which does not have the said drawback or has this drawback to a lesser extent.

According to the invention an arrangement provided with at least two series-arranged combustion flash bulbs in which said bulbs can be ignited one after the other and in which each of the bulbs includes a heating wire and an ignition paste, while a means is present in at least one bulb to render the internal resistance of said bulb one ohm at a maximum after flashing and the thermal capacities of the heating wires of the bulbs being substantially equal, is characterized in that prior to flashing the resistive values of the heating wires of the bulbs are different and this in such a manner that when arraying the bulbs in accordance with a decreasing resistance the heating wire of a subsequent bulb is 60 at a maximum of the resistance of the heating wire of the preceding bulb.

An advantage of this arrangement is that the electrical circuit thereof may be very simple. In fact, this circuit may only consist of a series arrangement of the relevant bulbs, while the connection conductors substantially do not include any further resistors.

A supply source is of course also required. It may consist of, for example, a batterywhose terminals are connected by the said series arrangement of bulbs. However, this leads to very fast successive flashing of the bulbs which may be desired, for example, for stroboscopic purposes. Due to the higher thermal development the bulb including the heating wire which had the highest resistance flashes first and subsequently the bulb flashes which includes the heating wire having the highest resistance but one, etc.

It is to be noted that it is known per se to give the flash bulbs of an arrangement provided with some flash bulbs a different resistance, for example, from U.S. Pat. No. 3,518,487. In this case, however, a parallel arrangement of bulbs was concerned in which external resistors had been added to each bulb.

In a preferred embodiment according to the invention, which is provided with a supply capacitor chargeable with an auxiliary device the capacitance of the supply capacitor has been chosen to be so low that the residual charge still present after flashing of a bulb in this supply capacitor corresponds to a quantity of energy which after multiplication by (Rh/Rt) is smaller than the energy required at that moment to ignite the remaining unflashed bulb having the highest resistance in the arrangement, where:

Rh is the resistive value of the heating wire of the said unflashed bulb having the highest resistance and Rt is the total resistive value of the discharge circuit of the supply capacitor.

Rt also includes the possible internal resistance of the supply capacitor.

An advantage of this preferred embodiment is that no double flashing (that is to say: two bulbs flashing almost simultaneously) can occur. This is advantageous when taking photographs.

The different resistive values of the flash bulbs (prior to flashing) may be realised, for example, by using a plurality of parallel-arranged heating wires in the bulbs in which, for example, the length of the heating wires is shortened to maintain the thermal capacity constant. These wires may then be made of, for example, the same material, but in one bulb of the arrangement the number of parallel heating wires may be chosen to be different from that in other bulbs of the arrangement' Instead of several parallel heating wires it is of course alternatively possible to use one heating wire having a larger thickness.

In a further special embodiment of an arrangement according to the invention the material of the heating wire of a bulb is different from the materials of the heating wires of the other bulbs.

An advantage thereof is that one heating wire which is not too thick may be sufficient for each bulb. This simplifies the manufacture of the bulbs.

In a very special embodiment of an arrangement according to the invention the heating wire of one bulb is made of kanthal and the heating wires of the other bulbs are made of chromel, alumel and molybdenum.

An advantage of this embodiment is that the specific heats of these materials (conductors) are fairly close so that also in case of mutually equal length and diameter of the heating wire the thermal capacity of the bulbs may be reasonably equal and the resistive values may be sufficiently different from each other.

In a further preferred embodiment of an arrangement according to the invention the said means to render the internal resistance of a bulb after flashing to a maxi- 3 mum of 1 ohm consists of an electrically conducting bush surrounding the supply conductors of the heating wire at an area located within the bulb, which bush melts upon flashing thereby shortcircuiting said supply conductors.

An advantage of this preferred embodiment is that switching over to a subsequent bulb may be very reliable.

The invention will further be described with reference to a drawing.

FIG. 1 is a diagrammatical view of an electrical circuit of an arrangement according to the invention.

FIG. 2 is a longitudinal cross-section through one of the combustion flash bulbs of the arrangement of FIG. 1.

In FIG. 1, l and 2 are input terminals intended to be connected to a charge device of the capacitor 3 including a resistor. The electrodes of the capacitor 3 are connected by means of a series arrangement ofa switch 8 and four low-voltage combustion flash bulbs 4, 5, 6 and 7.

The construction of these bulbs 4 to 6 is substantially identical. FIG. 2 shows such a bulb.

In FIG. 2, 10 is an envelope which is provided with two leadthrough conductors 11 and 12. These also pass through a bead 13 in which a metal bushing 14 is anchored. A heating wire 15 is present between the ends of the conductors 11 and 12 present in the envelope 10. The length of the bulb is approximately 25 mm and its diameter is approximately 9 mm.

The length of the heating wire 15 is approximately 1.4 mm and its diameter is approximately 25 microns.

In bulb 4 (see FIG. 1) the heating wire was made of kanthal, in bulb 5 it was chromel, in bulb 6 alumel and in bulb 7 molybdenum.

The table below states further data on these four heating wires. As the volumina of the wires were equal the ratio of the specific heat (see the table) also indicates the ratio of the thermal capacity of these wires.

4 ficients. This is the case in the embodiment described hereinafter. The safety margin for preventing double flashes is, however, amply sufficient in this case too.

In the envelope 10 of FIG. 2 some ignition paste was present on the heating wire 15. That paste has an ignition temperature of approximately 500C. Furthermore the envelope was filled with a wire filling 16 of zirconium.

The capacitor 3 (see FIG. 1) had a capacitance of approximately 200 p. Farad. This capacitor was charged to 6 volts. When the switch 8 closed for the first time the bulb 4 flashed. At a subsequent renewed charge of the capacitor 3, and a renewed closure of the switch 8, the bulb 5 flashed etc.

By flashing a bulb an interconnection between the leadthrough conductors (11 and 12) of this bulb was established by the bush 14 engaging these conductors which bush melted as a result of the thermal development. The interconnection obtained had a negligibly small resistance.

Other modifications of giving a flashed bulb a low resistance are likewise feasible.

Immediately after flashing the bulb 4 the residual voltage of the capacitor 8 was approximately 0.3 volt while the temperature of the heating wire of bulb 5 had increased to approximately 200C. This residual charge of the capacitor 8 was insufficient to heat the heating wire of the bulb 5 to 500C (being the ignition temperature of the paste).

This may also be explained as follows. Immediately after flashing the bulb 4 the residual energy in the capacitor was:

The quotient (Rh/Rt) was two-thirds at a maximum at that moment so that at a maximum 34; 9 1O Joule 6' 10' Joule was applied to the next bulb (bulb 5).

Considering the specific heat and the dimensions of the heating wire of chromel, of this bulb 5 (see the table), this may at most lead to an increase in the temper- The temperature coefficients included in the last column of this table are positive for the four heating wire materials considered. This means that for an increasing temperature the resistive values of the heating wires increase. This is favourable because this means that in the series arrangement of bulbs considered the resistance of the heating wire of the bulb at the instant of flashing that bulb, (which heating wire is then at a temperature of approximately 500C) is considerably higher than that of the heating wire of the bulb to be flashed next (which consequently has a temperature which is several hundred degrees Celcius lower). The occurrence of double flashes is then substantially excluded.

This favourable influence of the positive character of the temperature coefficients is slightly less if the bulbs having a low resistive value of the heating wire (at room temperature) have the highest temperature coefature of this wire by some degrees Celcius. In fact, the number of Joules necessary to raise the chromel wire by one degree of Celcius in temperature is:

Volume x specific heat 1r (25 10*) 1.4 X 3.93 10 Joule is approximately 3 l0 Joule.

An important advantage of an arrangement according to the invention is that all the parts to be heated, for example, for interconnection are present within the bulb envelopes so that their operation is very reliable.

What is claimed is:

1. A flash bulb assembly for cooperation with an associated camera providing sequential flashes, said assembly comprising a plurality of flash bulbs means connecting said flash bulbs in series each of said bulbs having a heating wire, two lead-through conductors connected to said ignition wire, and means for reducing the resistance between said lead-through conductors upon ignition of said bulb, one of said bulbs having a first resistance before ignition and a second resistance after ignition, a second of said bulbs having a third resistance before ignition and a fourth resistance after ignition, said third resistance being smaller than said first resistance.

2. The apparatus as described in claim 1 further including a third bulb, said third bulb having an ignition wire having a fifth resistance before ignition and sixth resistance after ignition, said fifth resistance being a less than said third resistance 3. The apparatus as described in claim 2 further including additional bulbs each having ignition wires having successively smaller resistances before firing than said other resistances.

4. The apparatus as described in claim 3 wherein said third resistance is not more than 60% of said first resistance, said fifth resistance is not more than 60% of said third resistance and each additional bulb has a resistance before ignition which is not more than 60% of every other resistance before ignition.

5. The apparatus as described in claim 4 wherein a resistance of each of said ignition wires before ignition is less than 1 ohm after ignition.

6. The apparatus as described in claim 4 wherein all said resistances are measured at room temperature.

7. The apparatus as described in claim 4 further including means for ignitin said bulbs, said means including a supply capacitor chargeable from an associated power supply, said capacitor having a capacitance sufficiently low so that the residual charge in said supply capacitor after flashing of one of said bulbs corresponds to a quantity of energy which after multiplication by the factor (Rh/Rt) is smaller than the energy required at that moment to ignite the remaining unflashed bulb having the highest resistance in said assembly, Rh being the resistive value of the unflashed lamp having the highest resistance in the assembly and Rt is the total resistive value of the discharge circuit of the supply capacitor.

8. The apparatus as described in claim 4 wherein the material of the heating wire of each of said bulbs is different from every other bulb in the assembly.

9. The apparatus as described in claim 4 wherein four bulbs are provided in said assembly and the material of the heating wires are kanthal, chromel, alumel and molybdenum.

10. The apparatus as described in claim 4 wherein said means for changing said resistance comprises an electrically conducting bushing which surrounds said supply conductors of the heating wire within said bulb, said bushing melting upon ignition of said bulb to complete. a circuit between said lead-through conductors.

UNITED STATES PATENT AND TRADEMARK OFFICE CETIFECATE OF CORRECTION PATENTNO.: 3,918,884

DATED 1 November 11, 1975 INV ENT0R(5) I JOHANNES G. BOK ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, in the TABLE "Temperature should read Temperature Coefficien Coefficient (a)/C.

last column line 3, "ll8.lO should read l88.l0

Claim 1, line 7, change "ignition" to --heating-;

Claim 2, line 2, change "an ignition" to a heating;

Claim 3, line 2, change "ignition" to heating-;

Claim 5, line 2, change "ignition" to heating-;

Claim 7, line 2, change "ignitin" to igniting.

I Signed and Scaled this Arrest:

RUTH c. MASON- Atlesring Officer 'C. MARSHALL DANN (nmmr'ssl'um'r nflarems and Trademarks 

1. A flash bulb assembly for cooperation with an associated camera providing sequential flashes, said assembly comprising a plurality of flash bulbs means connecting said flash bulbs in series each of said bulbs having a heating wire, two lead-through conductors connected to said ignition wire, and means for reducing the resistance between said lead-through conductors upon ignition of said bulb, one of said bulbs having a first resistance before ignition and a second resistance after ignition, a second of said bulbs having a third resistance before ignition and a fourth resistance after ignition, said third resistance being smaller than said first resistance.
 2. The apparatus as described in claim 1 further including a third bulb, said third bulb having an ignition wire having a fifth resistance before ignition and sixth resistance after ignition, said fifth resistance being a less than said third resistance.
 3. The apparatus as described in claim 2 further including additional bulbs each having ignition wires having successively smaller resistances before firing than said other resistances.
 4. The apparatus as described in claim 3 wherein said third resistance is not more than 60% of said first resistance, said fifth resistance is not more than 60% of said third resistance and each additional bulb has a resistance before ignition which is not more than 60% of every other resistance before ignition.
 5. The apparatus as described in claim 4 wherein a resistance of each of said ignition wires before ignition is less than 1 ohm after ignition.
 6. The apparatus as described in claim 4 wherein all said resistances are measured at room temperature.
 7. The apparatus as described in claim 4 further including meAns for ignitin said bulbs, said means including a supply capacitor chargeable from an associated power supply, said capacitor having a capacitance sufficiently low so that the residual charge in said supply capacitor after flashing of one of said bulbs corresponds to a quantity of energy which after multiplication by the factor (Rh/Rt) is smaller than the energy required at that moment to ignite the remaining unflashed bulb having the highest resistance in said assembly, Rh being the resistive value of the unflashed lamp having the highest resistance in the assembly and Rt is the total resistive value of the discharge circuit of the supply capacitor.
 8. The apparatus as described in claim 4 wherein the material of the heating wire of each of said bulbs is different from every other bulb in the assembly.
 9. The apparatus as described in claim 4 wherein four bulbs are provided in said assembly and the material of the heating wires are kanthal, chromel, alumel and molybdenum.
 10. The apparatus as described in claim 4 wherein said means for changing said resistance comprises an electrically conducting bushing which surrounds said supply conductors of the heating wire within said bulb, said bushing melting upon ignition of said bulb to complete a circuit between said lead-through conductors. 